A traditional vehicle navigation device has a route re-searching function (automatic re-routing function), so formed that when the vehicle is guided by searching a recommended route to a destination specified by a user and then out of the recommended route to change the route, the re-searching function automatically starts a re-searching to find a new recommended route so as to guide the vehicle to a destination through a changed route (see patent documents 1 and 2).
In patent document 1, when the navigation device detects a change of the route of the vehicle from the recommended route, a new recommended route is searched again and stored in a storage device. When a user instructs to start the route re-searching, a new recommended route stored in the storage device is displayed so as to guide a vehicle.
In patent document 2, when a vehicle traveling on a recommended route changes a lane before a branching point (for example, an intersection) and then travels for a specified time or longer on the changed lane, it will be determined that the vehicle is going to change its route from the recommended route, and the route re-searching is thus started. After the route change from the recommended route is confirmed, the new recommended route is displayed to guide the vehicle.
With regard to the route re-searching function disclosed in patent document 2, when a turning signal of the vehicle has been detected before the branching point for a specified time or longer, the route re-searching function will determine that the vehicle is going to turn right or left to change its route from the recommended route, thereby starting the route re-searching. After confirming that a route has been changed from the recommended route, the device may display a new recommended route searched beforehand, so as to guide the vehicle.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H09-152352
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-61356